Electric motors have been used for years with little concern being paid to the exhaust streams they produce. Typically, air-stream filtration concerns have been directed to the air intake vents of such motors, to prevent particulate from being introduced into the motors, where they could interfere with proper motor operation and possibly destroy the motor or its components. A variety of solutions to the air intake problems have been proposed, some of which are reflected in U.S. Pat. Nos. 1,009,951, 1,434,640, 1,750,446, 1,963,398, 1,963,401 and 2,205,128.
In contrast to air-intake concerns, the exhausts of electric motors have been given little attention. This has reflected both a lack of knowledge or awareness of the particulate emissions from electric motors, and a general belief that any such emissions were harmless.
In recent years, however, such concerns have been amplified because the brushes used in such motors degrade relatively quickly and in a manner that is likely to pollute the surrounding atmosphere (affecting indoor air quality) and foul equipment rooms. Graphite particles find their way into the air intakes of nearby equipment, leading to more frequent service calls, increased maintenance costs, and in the absence of careful maintenance (or even an awareness of the problem), costly equipment failure. Such failures may also be dangerous if they occur in elevator systems, which often use electric motors having graphite brushes. The placement of solid state equipment nearby to those motors increases concerns about pollutants, since such equipment is particularly vulnerable to breakdown or malfunction as a result of the intrusion of carbon dust.
Users of electric motors that employ graphite brushes have sought to overcome these problems by filtering motor exhaust vents. Thus, some users have wrapped motor exhausts in cloth bags to capture carbon particles generated by the degradation of brushes. Such bags, however, do a poor job of preventing carbon dust from entering the air stream, because of wide variability in the pore size of such cloth bags and poor fits to the motors. At the same time, such bags may also prevent inadequate air flow through the motor, causing an undesirable increase in motor temperature. Thus, motor users are in need of a new and different method of filtering electric motor exhaust streams.